The earliest chemical dust evolution in the solar nebula

The astrophysical aspects of the evolutionary path from dust to planets have been known for a long time but it was only recently that it could be followed by astronomical observations (Hubble Space Telescope). It was also recently that the mineral and chemical properties of dust around young stars in different stage of stellar evolution could be determined (the Infrared Space Observatory). Dust around these stars, including Vega-type stars that serve as an analog for the solar nebula, was identified as pure Mg-silicates (forsterite; enstatite), Fe-bearing and pure-Fe amorphous 'silicates', silica, Fe-metal, Fe-oxides (possibly Fe-sulfides) amorphous carbon and polycyclic aromatic hydrocarbons. They are the same phases that make up the aggregate and cluster interplanetary dust particles (IDPs) collected in the lower stratosphere. Recent vapor phase condensation experiments showed that the original condensates were mostly amorphous, chemically ordered, metastable eutectic 'FeSiO', 'MgSiO' and ferromagnesiosilica 'silicate' dust from which the observed non-carbon mineralogy could have evolved during hierarchical dust accretion in the solar nebula. The hypothesis of hierarchical dust accretion uses the size distributions for the surprisingly limited number of non-chondritic dust types in aggregate and cluster IDPs as a measure of relative time. It predicts the accretion of gradually larger, relatively younger, dust aggregates with increasingly diverse chemical and mineral properties of increasingly larger crystalline grains that evolved from initially mostly amorphous dust. This early chemical and mineral dust evolution can be traced in the collected aggregate and in larger cluster IDPs and in even larger aggregate meteoroids that burn up during atmospheric entry flash-heating but whereof the resulting Meteors contain information on the chemistry, grain size and texture of the original dust. These aggregate particles were protected against post-accretion, thermal or aqueous dust modification of the original presolar dust and the evolved mineralogy and chemistry during cold-storage inside icy protoplanets such as comet nuclei. The interplanetary dust particles provide ground truth to the properties and modification of the presolar dust in dense molecular clouds wherein stars, such as our sun, were born.